Deceleration of the solar wind in the Earth's foreshock region: Isee 2 and Imp 8 observations

Abstract

The deceleration of the solar wind, in the region of the interplanetary space filled by ions backstreaming from the earth's bow shock and associated waves, is studied using a two‐spacecraft technique. This deceleration, which is correlated with the ‘diffuse’ but not with the ‘reflected’ ion population, depends on the solar wind bulk velocity: at low velocities (below 300 km/s) the velocity decrease is ∼5 km/s, while at higher velocities (above 400 km/s) the decrease may be as large as 30 km/s. Along with this deceleration the solar wind undergoes a deflection by ∼1° away from the direction of the earth's bow shock. The energy balance shows that the kinetic energy loss far exceeds the thermal energy which is possibly gained by the solar wind; therefore at least part of this energy must go into waves and/or into the backstreaming ions.